<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
      <div id="app">
        <input type="text" :value="msg" @input="change">
        <!-- <input type="text" :value="msg" @input="$event.target.value"> -->
        {{msg}}
      </div>
      <script src="../js/vue.js"></script>
      <script>
          var app=new Vue({
             el:'#app',
             data:{
               msg:"qwer"
             },
             methods:{
              change(event){
                this.msg=event.target.value
              }
             }
          });
      </script>
</body>
</html>